Understanding the interplay between the crystal structure and charge transport in alloyed lead-free perovskites

In this work, we studied the impact of Pb-free perovskite compositions on various properties including the crystal structure, carrier mobility and lifetime, photoresponse in lateral devices, and photostability. We focused on a set of materials with the general formula MA3B2X9, where MA is the methylammonium cation, B stands for a Sb or Bi cation and X is a Br or I anion. I–Br alloying results in a structural modification from 0D to 2D configuration upon 40% Br addition. This structural change, however, did not impact carrier transport properties, while synthesis parameters have a strong impact on the carrier lifetime. Moreover, there is no direct correlation between the material dimensionality and responsivity values in lateral devices. Bi replacement with Sb as well as a low Br content is the key to high performance in photodetectors in a wide wavelength range. We also observe clear performance–stability trade-offs that the best-performing systems in lateral devices are the least stable due to the volatile nature of Sb atoms. Thus, when choosing a specific material for optoelectronics, one should trade between the two parameters, sacrificing either the responsivity or the lifetime of the device.